Austin continues fight with aquatic weeds

Last week, researchers at San Marcos, Texas-based Southwest Texas State University released 25 sterile grass carp into Lake Austin as part of Austin’s ongoing efforts to control the invasive weed hydrilla. The fish, which feed on the plant, are being studied as a possible solution for reducing the spread of the weed in the lake’s deep water.

Hydrilla covers more than 15 percent of the 1,600-acre lake’s surface and poses problems for recreational and navigational safety, fish and wildlife habitat, drinking water treatment and hydropower generation. The plant can grow up to one inch per day, forming dense mats that shade any plants below it. When the plant first was documented in the lake in 1999, it made up less than 9 percent of all vegetation in the lake; currently, it comprises 64 percent of the lake’s vegetation.

The Austin Watershed Protection and Development Review Department began combating hydrilla in January 2001 by lowering the lake’s water level 10 to 12 feet to dry out the plant in shallow areas and by installing gas permeable barriers along the exposed shoreline to prevent new growth. The city also has tried mowing and using herbicides to control the spread of the plant, but the hydrilla eventually grows back.

The Texas Parks and Wildlife Department approved a permit to allow the carp to be placed in the lake for the six-month study. Researchers will track the fish, which are marked with radio tags, to determine whether they will migrate to nearby lakes and rivers. “It is important to see if grass carp stay in Lake Austin or manage to go downstream,” says Mary Gilroy, an environmental scientist with the city’s Watershed Protection and Development Review Department. “If they stay in the lake, the Texas Parks and Wildlife Department could decide they are appropriate as one means to control the spread of hydrilla in Lake Austin and prevent it from spreading to other Central Texas waterways.”